Attempts have heretofore been made to control or improve the characteristics of optical devices, such as LEDs and LDs, by forming a periodic structure with a pitch almost the same as the wavelength of light on a surface or inside of the optical devices. The periodic structure for such purpose is produced in various ways of fine processing. Among such various ways of fine processing, nanoimprinting is one of the techniques that is now considered most promising. A mold (stamping die) used in a nanoimprint stamping die transfer process is usually manufactured by an optical exposure apparatus.
For molds used in a stamping die transfer process, not only planar molds used in planar pressing, but also roller-shaped molds (roller molds) which rotate to enable continuous transfer to a film have been developed. Conventional roller molds are manufactured by attaching a flexible material, such as a thin film of metal, to a roller. Such a mold has a cut line on the attached material and a pattern transferred therefrom may have a seam when the mold rotates 360 degrees. In order to avoid such problem, a pattern writing method combining exposure with the rotation of the roller mold has been used.
In the pattern writing that combines the roller mold rotation and exposure as described above, the conventionally-used methods of exposure include: a method of focusing an electron beam through a lens and irradiating a resist with the beam so as to write a pattern on the resist (see FIG. 11); and a method of irradiating a mask having an aperture pattern formed thereon with an electron beam which has been formed into substantially parallel light beams through a lens, so as to irradiate a resist with a plurality of electron beams that have passed through the mask, thereby simultaneously writing a pattern with the electron beams on the resist (see FIG. 12).
Further, examples of the method for writing a pattern by combining the roller mold rotation and exposure include: (1) a method of writing a groove-like pattern by continuously rotating the roller mold (see FIGS. 13A and 13B, such mold pattern is sometimes called a “line-and-space” pattern due to its form); and (2) a method of exposing a certain area of the roller mold with rotation of the roller mold being stopped and then feeding the roller mold at a predetermined angle in order to expose the next area, so as to sequentially write a predetermined pattern (mask pattern) in the circumferential direction on the roller mold, and, after a 360-degree rotation of the roller mold, moving in the axial direction and similarly performing the sequential exposure of the roller mold in the circumferential direction in order to write the predetermined pattern thereon (see FIGS. 14A and 14B, such method is sometimes called a “step-and-repeat” method due to its form).
With regard to the latter method (step-and-repeat), a technique has been proposed in which, when a repeated pattern (mask pattern) on the original substrate is transferred by exposure onto a side surface of a sample which is to be exposed, a step of exposure and a step of rotating the sample such that the side surface of the sample rotates by a distance corresponding to one cycle of the repeated pattern (mask pattern) are repeated alternately in order for the repeated mask pattern to be formed on the side surface of the sample with a high level of spacing accuracy (see, for example, Patent Document 1 below).